The present invention relates to improving the efficiency of an internal combustion engine and in particular to a muffler which reduces exhaust system back pressure to improve engine performance.
The increasing cost of oil has motivated car owners and manufacturers to seek means to improve vehicle mileage. In particular, auto manufacturers seek to increase their market share and to satisfy government mileage requirements. Improvements to exhaust systems in the form of reduced restriction and tuned lengths have become commonplace and vehicle mileage has somewhat benefitted from such efforts. However, meeting federally mandated mileage requirements remains a challenge and further improvements are necessary.
Reducing pollution continues to be an important societal objective. Pollution levels in metropolitan areas remain unacceptably high at times, and create an immediate direct health issue for humans, and a longer term issue due to the damage to plant life. Automotive-based pollution remains an issue, and auto makers are continually challenged to reduce the emissions from new automobiles. Further, the emissions from older vehicles continue even if new vehicles achieve significant emission reductions.
Modern automobiles greatly benefit from Electronic Fuel Injection (EFI) systems and efficient intake manifold and head designs. As a result, new automobiles have greatly improved economy and reduced emissions. But while the intake aspect of engine design has advanced drastically, exhaust systems have not similarly advanced. U.S. Pat. No. 6,213,251 issued Apr. 10, 2001 for “Self Tuning Exhaust Muffler,” describes a muffler having an outer tube and an inner louver tube, wherein a spiral vane extends outwardly from the louver tube to the outer tube and forms a helical passage for a flow between the louver tube and the outer tube. A multiplicity of “scoops” on the inside wall of the louvered tube “scoop” an outer portion of the flow through the louvered tube into the helical passage.
U.S. Pat. No. 6,679,351 issued Jan. 20, 2004 for “Air Turbine for Combustion Engine,” describes an “air turbine” apparatus creating a rotational flow which creates a muffling effect without restricting flow. The apparatus of the '351 patent includes annular recesses (or convolutions) at the forward end (i.e., before the diameter increases) of the apparatus, which are intended to create a cyclone or vortex effect in the air flow. Following the annular recesses, the air flow enters an expansion chamber, wherein an airfoil is positioned at the front of the expansion chamber to split the air flow into a high velocity lower pressure outer vortex, and a lower velocity higher pressure inner vortex. The air foil is shown in several figures of the '351 patent, and clearly plays the dominant role in the flow characteristics of a muffler according to the '351 patent and is essential to the described invention. Further, in column 4, lines 22-25, the '351 patent states that “the ratio of air passing around the airfoil compared to the air passing through the airfoil for a six inch diameter expansion chamber is approximately 2.7 to 1,” indicating that the air foil plays the dominant role on controlling air flow through the muffler. Additionally, FIG. 10 of the '351 patent shows an embodiment of the invention of the '351 patent which essentially consists of the annular rings and the airfoil, and the inner tube 22 is entirely absent.
Although attempts have been made to improve performance and efficiency through modifications to exhaust systems, there remains a need to improve overall engine performance, improve mileage, and reduce pollution.